Introduction to Anatomy & Physiology: Organization, Homeostasis, and Anatomical Terminology

Anatomy and Physiology: Definitions and Scope

Overview

Anatomy is the study of the structure of body parts and their relationships to one another. Physiology is the study of the function of body parts; how they work to carry out life-sustaining activities. Both disciplines are closely linked, as structure often determines function.

Subdivisions of Anatomy

• Gross or macroscopic anatomy: Study of large, visible structures.

• Regional anatomy: Study of all structures in a particular area of the body (e.g., muscles, bones, nerves).

• Surface anatomy: Study of internal structures as they relate to the overlying skin surface.

• Microscopic anatomy: Study of structures too small to be seen with the naked eye (e.g., cells, tissues).

• Developmental anatomy: Study of structural changes throughout the lifespan.

• Embryology: Study of developmental changes before birth.

Subdivisions of Physiology

• Based on organ systems (e.g., renal or cardiovascular physiology).

• Focuses on the functions of specific organs and systems.

• Cellular and molecular physiology: How cells and molecules interact to support life.

Principle of Complementarity of Structure and Function

Explanation

Structure and function are closely related in the human body. What a structure can do depends on its specific form. This principle is fundamental in understanding anatomy and physiology.

Levels of Structural Organization

Hierarchy

• Chemical level: Atoms combine to form molecules.

• Cellular level: Cells are made up of molecules.

• Tissue level: Tissues consist of similar types of cells.

• Organ level: Organs are made up of different types of tissues.

• Organ system level: Organ systems consist of different organs that work together closely.

• Organismal level: The human organism is made up of many organ systems.

Requirements for Life

Maintenance of Boundaries

• Separation between internal and external environments must exist.

• Plasma membranes separate cells.

• Skin separates organism from environment.

Movement

• Muscular system allows movement.

• Of body parts via skeletal muscles.

• Of substances via cardiac muscle (blood) and smooth muscle (digestion, urination).

• Contractility refers to movement at the cellular level.

Responsiveness

• Ability to sense and respond to stimuli.

• Withdrawal reflex prevents injury.

• Control of breathing rate, which must change in response to different activities.

Digestion

• Breakdown of ingested foodstuffs, followed by absorption of simple molecules into blood.

Metabolism

• All chemical reactions that occur in body cells.

• Sum of all catabolism (breakdown) and anabolism (synthesis of molecules).

Excretion

• Removal of wastes from metabolism and digestion.

• Urea (from breakdown of proteins), carbon dioxide (from metabolism), feces (undigested food).

Reproduction

• At the cellular level, reproduction is the production of offspring.

• At the organismal level, reproduction is the production of a new individual.

Growth

• Increase in size of a body part or of organism.

Necessary Life Functions

Humans are multicellular; to function, individual cells must be kept alive. Organ systems are designed to service the cells. All cells depend on organ systems to meet their survival needs.

Organ Systems Overview

Major Organ Systems and Their Functions

System	Main Function
Integumentary	Protects the body, regulates temperature, prevents water loss
Skeletal	Supports and protects organs, provides framework for movement
Muscular	Allows movement, maintains posture, produces heat
Nervous	Fast-acting control system, responds to internal/external changes
Endocrine	Secretes hormones for growth, reproduction, metabolism
Cardiovascular	Transports blood, oxygen, nutrients, wastes
Lymphatic	Returns fluid to blood, disposes debris, immune response
Respiratory	Keeps blood supplied with oxygen, removes carbon dioxide
Digestive	Breaks down food, absorbs nutrients, eliminates waste
Urinary	Eliminates nitrogenous wastes, regulates water/electrolytes
Male Reproductive	Produces sperm, male sex hormones
Female Reproductive	Produces eggs, female sex hormones, supports fetal development

Survival Needs

• Nutrients: Chemicals for energy and cell building.

• Oxygen: Essential for release of energy from food.

• Water: Most abundant chemical in the body, provides environment for chemical reactions.

• Normal body temperature: If body temperature falls below or goes above 37°C, rates of chemical reactions are affected.

• Appropriate atmospheric pressure: Specific pressure is needed for adequate breathing and gas exchange in lungs.

Homeostasis

Definition and Importance

Homeostasis is the maintenance of a relatively stable internal environment despite continuous changes in the environment. It is a dynamic state of equilibrium, always readjusting as needed, and is maintained by contributions of all organ systems.

Homeostatic Control Mechanisms

• Receptor (sensor): Monitors environment, responds to stimuli.

• Control center: Determines set point, receives input from receptor, determines appropriate response.

• Effector: Receives output from control center, provides the means to respond, response either reduces (negative feedback) or enhances (positive feedback) stimulus.

Negative Feedback

• Most feedback mechanisms in the body are negative feedback.

• Response reduces or shuts off original stimulus.

• Examples: Regulation of body temperature (nervous system), regulation of blood glucose by insulin (endocrine system).

Example: Regulation of Blood Glucose

• Receptors sense increased blood glucose (blood sugar).

• Pancreas (control center) secretes insulin into the blood.

• Insulin causes body cells (effectors) to absorb more glucose, which decreases blood glucose levels.

Positive Feedback

• Response enhances or exaggerates the original stimulus.

• May exhibit a cascade or amplifying effect.

• Usually controls infrequent events that do not require continuous adjustment (e.g., enhancement of labor contractions by oxytocin, platelet plug formation and blood clotting).

Homeostatic Imbalance

• Disturbance of homeostasis increases risk of disease.

• Contributes to changes associated with aging.

• If negative feedback mechanisms become overwhelmed, destructive positive feedback mechanisms may take over (e.g., heart failure).

Anatomical Terminology

Body Regions and Directional Terms

• Cephalic: Refers to the head and face.

• Cervical: Refers to the neck.

• Thoracic: Refers to the chest.

• Abdominal: Refers to the abdomen.

• Pelvic: Refers to the pelvis.

• Upper limb: Includes arm, forearm, wrist, and hand.

• Manus: Refers to the hand.

• Lower limb: Includes thigh, leg, ankle, and foot.

• Pedal: Refers to the foot.

• Dorsal: Refers to the back.

Directional Terms

• Superior (cranial): Toward the head or upper part of a structure.

• Inferior (caudal): Away from the head or toward the lower part of a structure.

• Anterior (ventral): Toward the front of the body.

• Posterior (dorsal): Toward the back of the body.

• Medial: Toward the midline of the body.

• Lateral: Away from the midline of the body.

• Intermediate: Between a more medial and a more lateral structure.

• Proximal: Closer to the origin of the body part or the point of attachment.

• Distal: Farther from the origin of a body part or the point of attachment.

• Superficial (external): Toward or at the body surface.

• Deep (internal): Away from the body surface; more internal.

Body Planes

• Frontal (coronal) plane: Divides the body into anterior and posterior parts.

• Transverse (horizontal) plane: Divides the body into superior and inferior parts.

• Median (midsagittal) plane: Divides the body into right and left halves.

Body Cavities

• Dorsal body cavity: Contains the cranial cavity and vertebral cavity.

• Ventral body cavity: Contains the thoracic cavity and abdominopelvic cavity.

Additional info: Some explanations and examples have been expanded for clarity and completeness, including the table of organ systems and their functions.